How about making entire field groups conditional? See field groups module for D7
And how about integration with multistep? http://drupal.org/project/multistep for D7
Imagine setting a value A on step 1 of a multistep content type form. Now I want fields on step 2 to be hidden. I don't think this works well.

I have this need as well ! That's really, IMHO, a must for the sake of using Drupal as a web application engine. In my case, I am building a booking web app and the "booking" content type would be optimum with this feature. At the moment I cannot gather fields logically and the ergonomy suffers from that.